Engine synchronizer



Nov. 25, 1969 R. NELSON ET AL. 3,479,822

ENGINE SYNCHRONIZER 3 Sheets-Sheet l Filed March 27, 1968 "14 AGENT Nov. 25, 1969 R. E. NELsoN Y ETA-1 ENGINE SYNCHRONIZER 3 Sheets-Sheet 2 M. w`l

l Filed March 27, 1968 NOV. 25, 1969 R. E. NELSON ET AL 3,479,822

ENGINE SYNCHRONIZER 'Filed March 27, i968 3 Sheets-Sheet 5 .n d o Alli moza mhwsz United States Patent C) 3,479,822 ENGINE SYNCHRONIZER Robert E. Nelson, Indianapolis, and Charles D. Boltz, Jr.,

Greenwood, Ind., assignors, by mesne assgnments, to

the United States of America as represented by the Secretary of the Navy Filed Mar. 27, 1968, Ser. No. 716,657 Int. Cl. F021; 73/00;F01b 21/00; B64c 1]/46 US. Cl. 60-97 7 Claims ABSTRACT OF THE DISCLOSURE A control system which provides for speed synchronizing and phase synchronizing two or more turboprop engines by applying current to the windings of a torque motor which is attached to the fulcrum point of the engine governor system. By energizing the torque motor in a direction to aid or oppose the centrifugal governor weight, more or less propeller pitch may be essentially artificially introduced to increase or decrease motor speed.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION When two or more engine-propeller combinations are rotating at slightly different speeds, a vibration beat drevelops, the frequency of which is dependent upon the speed difference which exists between the engines. To eliminate the detrimental effects of vibration beat and noise in an aircraft, automatic synchronizer mechanisms are employed to maintain the engines in speed synchronism with each other. In addition, it has been found desirable both from the vibration and the noise standpoint not only to synchronize the several engine propellers as to speed but also to maintain a selective phase relation between the propellers themselves. Mechanisms responsive to speed alone are not capable of maintaining the required phase relationship even when such mechanisms are capable of maintaining speed synchronization.

SUMMARY OF THE INVENTION In order to accomplish the above desired results, applicant has invented a new and improved synchronizing circuit which automatically, accurately, and electronically synchronizes a plurality of engines not only for speed but also for phase.

There are three operational modes of the control: damping, speed synchronization, and phase synchronization. The damping mode provides a signal to reduce the effect of sudden changes in propeller speed due to transient loading conditions, and provides a stabilizing factor for power transients. The damping signal is developed by differentiating the voltage which represents propeller, or turbine speed. Steady state speeds develop no signal, but sudden changes in speeds cause a large opposing signal voltage to be developed.

The speed synchronization mode of operation is one in which the control acts only to provide speed synchronization of the slave engine with the master engine.

It is actually a bias function where a signal representing the difference in speed of the two engines is used to provide a bias level for the operation of the control. The synchronizing signal is obtained by integration of the signal which respresents the different between engine speeds. The operation of the integrator is such that its output keeps increasing as long as the slave engine speed is greater than the master engine speed, and it decreases as long as the slave engine speed is less than the master engine speed. The integrator output voltage remains constant only when the two speeds are equal and during the synchronization mode of operation, the damping function is also provided to aid in speed stabilization.

The phase synchronization mode is the mode whereby phase synchronization of the master engine propeller and the slave engine propeller actually takes place. This mode fulfills the design objective of the control. A degree of redundancy exists somewhat in the speed synchronizing and the phase synchronizing modes in that one would expect the propellers to be synchronized when the engine speeds are synchronized. The speed synchronization mode actually affects a very tight governing control mode. Speed synchronization is eifectively obtained to the degree of zero average speed error. In the absence of any transient conditions, a degree of blade phase synchronization is attained in this mode. `In reality, however, transients do cause momentary speed differences, and propeller phase runout, which can be controlled only by the signals applied during the phase synchronization mode. The speed synchronization mode is therefore used to obtain propeller speed synchronization and a reasonably stable phase relationship. Once the propeller speeds have been synchronized by the speed synchronization mode, however, the control can be placed in the phase synchronization mode. In this mode two new signals come into play which accomplish a phase synchronization of the two propellers. A signal representing the difference between the engine speeds is used to help maintain speed synchronization, and a signal which represents the phase difference between the blades of the slave propeller and their respective counterparts on the master propeller, are summed to provide a very tight control signal. In the phase synchronization mode of operation there is no speed synchronization signal applied; the damping signal is provided. however, to assist in stabilization. In addition, a signal which represents the integral of phase angle is provided to eliminate the droon allowed by the proportional phase signal.

An object of the present invention is the provision of the engine synchronizing circuit which obtains synchronization of a plurality of engines both as to speed and phase.

Another object of the invention is the provision of a damping mode to reduced the effect of sudden changes in propeller speed due to transient loading conditions.

Another object is the provision of a synchronizing circuit which energizes a torque motor attached to the fulcrum point of the speed governor.

A further object is the provision of a synchronizing circuit for reducing the noise and beat frequency in the aircraft cabin.

Still another object is the provision of a synchronization circuit which provides three operational modes of control.

Yet another object of the invention is the provision of a synchronization circuit in which the synchronizing signal is obtained by integration of a signal which represents the difference between engine speeds.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. l shows a block diagram of the over-all system;

FIG. 2 shows a block diagram of the speed synchronizing circuit;

FIG. 3 shows the waveforms present in the synchronizing circuit;

FIG. 4 shows a block diagram of the phase synchronizing circuit; and

FIG. 5 shows a block diagram of the damping circuit.

Referring now to FIG. 1, there will be seen the three major circuits which are responsible for the three modes of operation of the device; namely, a speed synchronizing circuit 11, a phase synchronizing circuit 12, and a damping circuit 13. The speed synchronizing circuit 11 has two inputs, one from a master trigger circuit 14, and the other from a slave trigger circuit 15. The output of speed synchronizing circuit 11 passes through an integrating circuit 16 and is applied to one of the arms of phase synchronizing relay 17a. From the phase synchronizing relay the signal then passes to a mixer 18 and is finally applied to an amplifier 20. Torque motor 21 is connected to the output of amplifier 20 so that action of the motor is responsive to the ampliliers output.

An alternate output from phase synchronization relay 17a leads to synchronization relay 22, the arm of this relay in turn being connected to a mixer 23, the output of which serves as an input to an integrator 24. The output of integrator 24 then leads to another mixer 25 whose output is applied as a second input to amplifier 20.

Turning now to the damping channel, it will be seen that the output of slave trigger circuit in addition to being applied to component 11, is also applied as an input to damping circuit 13, the output of this circuit being in turn applied to an amplifier 26 Whose output forms another input to mixer 25. Connected across motor 21 is a damping relay 27.

The third and final mode of operation, that of phase synchronization, results when a signal from the master propeller position circuit 28 and a signal from the slave position propeller circuit 29 are both applied as inputs to the phase synchronizer circuit 12. The output of phase synchronizing circuit 12 is applied to relay contact 17b where the signal is split into two channels, a portion of the signal being applied to mixer 23 and the other portion of the signal being applied to mixer 18.

Referring now to FIG. 2, there will be seen a block diagram of the speed synchronizing circuit 11. Here master trigger signal 14 and slave trigger signal 15 are both applied as inputs to a flip flop 31 the output of which is applied to an RC filter 32. The output of filter 32 is divided into two parallel channels one of which consists of an inverter and diferentiator 33, a diode rectifier 34, a trigger generator 35, a one-shot multivibrator 36, and a positive pulse amplifier 37. The other channel consists of a differentiator 38, diode rectifier 39, trigger generator 41, one-shot multivibrator 42, and a negative pulse amplifier 43. The outputs of both of these parallel channels, positive pulse amplifier 37 and negative pulse amplifier 43, are applied to filter 16 (FIG. 1) from which the signal is applied to synchronizing relay 17a.

In FIG. 4 there is shown a block diagram of the phase sensing and integration board including the phase synchronization circuit 12 shown in FIG. l. A magnetic pickup device 28, which is activated by the master propeller as it rotates, generates a signal which is applied to a trigger generator 44 the output of which is applied to a fiip-tlop 46. Likewise, magnetic pickup 29, which is activated by the slave propeller as it rotates, generates a signal which is applied to a trigger generator 45, the output of which is also applied as an input to flip-flop 46. The output of fiip-ffop 46 is divided into two parallel channels, one of which is a positive amplifier 47 and the other a negative amplifier 48, the output of these amplifiers being combined and applied across a potentiometer 50. The sliding arm of potentiometer 50 picks up the combined signal and applies it to a filter 51 and in turn to a limiter 52 before it is applied to phase synchronization relay 17b (FIG. l).

The elements making up the damping circuit 13 and the associated components therewith are shown in block diagram in FIG. 5. The slave trigger 15 is applied to a trigger amplifier 53, a pulse width control circuit 54, a pulse amplifier 55, a filter circuit V56, and an emitter follower 57 before being applied to a differentiator 58- and an operational amplifier 26 (FIG. 1). The output of arnplifier 26 is then applied via mixer 25 and amplifier 20 to the motor windings 21.

Referring now to the operation of the device by a description of the three operational modes of control, that is, speed synchronization, phase synchronization and damping, it can be seen that fiip-fiop circuit 31 is Set by the master speed trigger 14 and is reset by the slave speed trigger 15. These triggers are generated by torque pickup devices associated with each of the motors and it will be assumed that the repetition rate of these triggers is proportional to their respective engine r.p.m.s. Traces A through G of FIG 3 illustrate a situation where the slave engines speed is greater than the master, and traces H through P illustrate the situation where the slave speed is lower than the master. As the flip-flop 31 is triggered alternately from one stable state to the other, the Waveforrns of trace C and trace K will result. This signal is then filtered by filter 32 to divide the signals shown by trace D and trace L. These sawtoooth waveforms are a result of phase slippage, or speed differences, between the two engines as the speeds approach synchronization; that is, as slave speed minus master speed approaches Zero, the frequency of the sawtooth Waveform decreases toward zero, and only at speed synchronization does the sawtooth actually disappear.

Thus the sawtooth created after it has been filtered by filter 32 is applied as inputs to inverter differentiator 33 and the diferentiator 38, the sawtooth thus created being inverted by inverter 33. This circuit forms a portion of the polarity sensing function of the sawtoooth. Each of the delay multivibrators is triggered by the negative going step from the sawtooth waveform. It is for this reason that the inverted waveform is used to generate a trigger at trigger generator 35. The sawtooth waveform of trace E, FIG. 3, is differentiated by dierentiator 33 and the negative spike produced, causes a trigger pulse to be generated by trigger generator 35 (trace G). In the other channel the waveform of trace I., FIG. 3, is differentiated by differentiator 38, and the negative spike produced causes a trigger pulse to be generated by trigger generator 41. Note that triggers are produced at generator 35 only when slave speed is greater than master speed, and that triggers are produced at trigger 41 only when master speed is greater than slave speed. The one-shot multivibrator 36 is triggered by the puse from generator 35, While the multivibrator 42 is identical to the one triggered by 35 except that it is triggered by 41. The output of multivibrator 36 drives a positive pulse amplifier' 37 to produce a positive pulse which is applied at the collector of the output stage of negative pulse amplifier 43 while the outputs of multivibrator 42 drives negative pulse amplifier 43 to produce a negative pulse also at the collector of the final stages of that component. The Waveform at this point is therefore a series of positive or negative pulses proportional to slave speeds minus master speed, both in polarity and frequency. Their pulse Width is constant and determined by the one-shot multivibrators 36 and 42. The filter network 16 which is connected to the collector of the final stage of amplifier 43 is used to provide a DC signal proportional to slave speed minus master speed.

The phase synchronization mode of operation, as shown in block diagram form in FIG. 4, is accomplished by a magnetic pickup located on the engine gear box in close proximity to the propeller shaft, so that the pickup senses the passage of a metal slug which is indexed with respect to a blade of the propeller. The trigger thus generated provides information regarding the propeller position. This information is converted to a signal which represents the phase difference between the master engine propeller and the slave engine propeller. Thus, the pulse from the master engine pickup 28 is converted to a trigger by trigger generator 44 which is used to reset the ip-flop circuit 46 while the pulse, and subsequent trigger from the slave engine pickup 29 and trigger 45, sets the iiipfiop 46. A zero phase relationship between master propeller and slave propeller in reality is a 180 relationship in terms of one revolution of the propeller. The flip-op 46 is triggered once per revolution of each propeller, therefore with 180 relationship, the ip-op output is a square wave with a 50 percent duty cycle. As the phase relationship between propellers changes, the duty cycle of the flip-flop varies proportionately. The positive going portion of the iiip-flop 46 output causes a positive voltage to appear at the output of positive amplifier 47, while the negative portion of the ip-op output causes a negative voltage to appear at the output of negative amplifier 4S. These outputs are impressed across a phase adjust potentiometer 50, such that the final signal is a function of true propeller phase, and potentiometer position. The rectangular waveform from the potentiometer is filtered by lter 51 to provide a DC signal proportional to propel- 1er phase angle and is clamped by limiter 52 to limit the maximum signal output from the circuit. The signal produced by this cricuitry is the propeller phase signal and is passed on to relay 17b.

The damping mode of operation, shown in blank form in FIG. 5, can be thought of as the transient suppression or the speed stabilization function of the control. A pulse from the slave engine trigger circuitry is fed to an amplifier circuit S3. The following stage is a pulse width control circuit 54 which is composed of two stages, 54a and 541), and the pulse produced by trigger ampliier 53 turns on stage 54a for a very short duration, but long enough to charge a particular condenser to minus 25 volts. As long as the condenser has a negative charge, stage 5417 is biased off. When the shock pulse disappears from its input, stage 54a returns to its non-conducting state and the condenser begins charging towards positive 25 volts high voltage. When its charge voltage approaches approximately plus 1 volt, stage 54b is biased to on the ON condition. The OFF time of stage 541: is thus determined by the time constant of an RC circuit made up of a resistance and the particular condenser mentioned. This circuit functions somewhat as a one-shot multivibrator, but it has the advantage of b.^ing capable of greater than 100 percent duty cycle, since it has effectively a negative reset time in that it can be trigered at any time during its cycle and the resulting time delay will be a constant starting at the trigger pulse. The constant width pulse produced by the circuit 54 is then amplified by pulse amplifier 55 and filtered by filter 56. The resulting DC signal is a voltage proportional to the slave engine speed. The damping circuit, therefore, merely functions as a frequency DC converter. The emitter follower 57 prevents loading of the filter circuitry 56 and provides a low driving impedance for differentiating capacitor 58. Since the speed signal is differentiated by 58, the signal at this point represents only the changes in speed with respect to time. After the speed signal leaves difierentiator 58, it is amplified by amplifier 26 whose output is then passed on to mixer 25.

The circuitry which makes up the master trigger signal 14 and the slave trigger signal 15 consists simply of two identical trigger amplifiers which accept inputs from the torque meter pickups of the slave and master engines, and provide output pulses for each of the input pulses sufficient to drive the appropriate control circuitry. The input signals are generated by the passage of torque meter excited teeth in close proximity to the torque meter pickup, the exciter being a gear-like disk attached to the engine drive shaft, and the torque meter pickup being a fairly conventional magnetic-type sensing device. The output of these trigger ampliers comprise a signal from master trigger circuits and slave trigger circuits 14 and 15 and applied at inputs to phase synchronizing circuit 11.

The output circuitry of the device is an operational amplifier 20 with a driver output stage which converts the voltage out of the amplifier to a current sufficient to drive the torque motor 21 in the propeller governor.

From the above description of the structure and operation of the present invention, it is obvious that the device offers a vast improvement over prior art synchronizing systems. Not only will the invention provide speed synchronization of two propellers but it will also provide phase synchronization and damping against sudden changes in propeller speed due to transient loading conditions. The device accomplishes its synchronizing function entirely electronically, is extremely sensitive and is quick acting so that in the event of even small differences between the master and slave engines the device rapidly compensates for this difference accurately and with a minimum of overshoot.

What is claimed is:

1. An electronic propeller control system comprising means for generating a signal indicative of master engine speed;

means for generating a signal indicative of slave engine speed;

means for applying the master speed signal and the slave speed signal to a speed synchronizing circuit; means for generating a signal indicative of propeller position of the master engine;

means for generating a signal indicative of propeller position of the slave engine;

means for applying the master position signal and the slave position signal to a phase synchronizing circuit;

means for applying the slave speed signal to a damping circuit; and

motor means on the slave engine for receiving the output of the speed synchronizing circuit, the phase synchronizing circuit, and the damping circuit for synchronizing the slave engine with the master engine.

2. The system of claim 1 wherein the means for generating a signal indicative of master engine speed consists of a torquemeter pickup attached to the master engine with the output of the torquemeter driving a trigger generator.

3. The system of claim 2 wherein the means for generating a signal indicative of slave engine pickup consists of a torquemeter pickup attached to the slave engine with the output of the torquemeter driving a trigger generator.

4. The system of claim 3 wherein the speed synchronizing circuit comprises a ip-iiop circuit which is alternately triggered from one stable state to the other stable state by the master speed signal and the slave speed signal;

parallel signal channels fed by Hip-flop, each channel having a diierentiator, a trigger generator, a multivibrator, and a pulse amplifier so that one channel produces a positive pulse and the other channel produces a negative pulse; and

means for combining the positive and negative pulses to produce a signal indicative of the speed difference between the master and slave engines.

5. The system of claim 4 wherein the phase synchronizing circuit comprises a iiip flop circuit which is alternately triggered from one stable state to the other stable state by the propeller position signal from the master and slave engines;

a positive amplifier and a negative amplier connected to the output of the flip op; and

a potentiometer connected to the output of the two ampliers to produce a signal proportional to the propeller phase angle.

6. The system of claim 5 wherein the damping circuit comprises a trigger amplifier, a pulse width control circuit, a pulse amplifier, an emitter follower, and a differentiator, all connected in series to produce a signal proportional to slave engine speed.

7. The system of claim 6 wherein the motor means is UNITED STATES PATENTS 6/1951 Nichols N0-135.29 8/1958 Clark 60-975 XR MARTIN P. SCHWADRON, Primary Examiner R. R. BUNEVICH, Assistant Examiner U.S. Cl. XR. 170--l35-29 

